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//===---------------------- shared_mutex.cpp ------------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is dual licensed under the MIT and the University of Illinois Open
// Source Licenses. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#define _LIBCPP_BUILDING_SHARED_MUTEX
#include "shared_mutex"
_LIBCPP_BEGIN_NAMESPACE_STD
shared_mutex::shared_mutex()
: __state_(0)
{
}
// Exclusive ownership
void
shared_mutex::lock()
{
unique_lock<mutex> lk(__mut_);
while (__state_ & __write_entered_)
__gate1_.wait(lk);
__state_ |= __write_entered_;
while (__state_ & __n_readers_)
__gate2_.wait(lk);
}
bool
shared_mutex::try_lock()
{
unique_lock<mutex> lk(__mut_);
if (__state_ == 0)
{
__state_ = __write_entered_;
return true;
}
return false;
}
void
shared_mutex::unlock()
{
lock_guard<mutex> _(__mut_);
__state_ = 0;
__gate1_.notify_all();
}
// Shared ownership
void
shared_mutex::lock_shared()
{
unique_lock<mutex> lk(__mut_);
while ((__state_ & __write_entered_) || (__state_ & __n_readers_) == __n_readers_)
__gate1_.wait(lk);
unsigned num_readers = (__state_ & __n_readers_) + 1;
__state_ &= ~__n_readers_;
__state_ |= num_readers;
}
bool
shared_mutex::try_lock_shared()
{
unique_lock<mutex> lk(__mut_);
unsigned num_readers = __state_ & __n_readers_;
if (!(__state_ & __write_entered_) && num_readers != __n_readers_)
{
++num_readers;
__state_ &= ~__n_readers_;
__state_ |= num_readers;
return true;
}
return false;
}
void
shared_mutex::unlock_shared()
{
lock_guard<mutex> _(__mut_);
unsigned num_readers = (__state_ & __n_readers_) - 1;
__state_ &= ~__n_readers_;
__state_ |= num_readers;
if (__state_ & __write_entered_)
{
if (num_readers == 0)
__gate2_.notify_one();
}
else
{
if (num_readers == __n_readers_ - 1)
__gate1_.notify_one();
}
}
_LIBCPP_END_NAMESPACE_STD
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